From official release note: UI: Fixed the issue where the vertices were not stripped for rich text in multi line. (1182818)
This fix in 2018.4.26 break this plugin. Already sumbit a ticket to Unity support but they said this is not a bug, but they do point out the cause and suggest to update the plugin.
I'm still looking into the code, figuring how to fix it since I'm not familiar with this part.
The author has no reactions after 2018, so I guess can't depend on him.
Post an issue here to remind anyone trying to use this plugin.